1. Field of Invention
This invention relates generally to tire/vehicle systems designed for four-wheeled automotive vehicles, and specifically for such systems wherein a portion of the rear tire tread tracks a front tire tread.
2. Description of the Prior Art
In automotive vehicles, proper traction between the tire and the road surface is necessary for effective operation of the vehicle. Under certain weather conditions, such as rain, the traction of the tire on the road surface can be impaired. For example, a vehicle traveling on a rain-soaked road surface at high speed can "hydroplane" and lose contact with the road surface altogether. For this reason, it is desirable that tires be able to channel water away from the footprint of the tire to ensure good traction between the tire and road surface. U.S. Pat. No. 4,545,415 discloses a tire tread designed to provide good traction on slippery road surfaces.
A second problem is that four-wheeled vehicles are usually fitted with identical tires at all four wheel positions even though the operating conditions and performance requirements at each wheel may be different. For example, the functions necessarily performed by each tire, such as steering, load bearing, and transmitting driving torque from the engine to the road surface are usually different at each wheel position.
Some tire designers have sought to maximize vehicle performance by tuning each tire to its wheel position. German Patent No. 1,480,962 discloses a front and rear tire combination in which the compound in the front tire is different from that in the rear tire, the combination designed to improve treadwear. German Patent No. 2,536,470 discloses a front and rear tire combination in which the tread pattern on the front tire is varied slightly from the tread pattern on the rear tire to limit the noise generated by the combination. Japanese Patent No. 58-164360 discloses a front and rear tire combination in which the tread pattern of the front tire differs from that of the rear tire in order to maximize the cornering characteristics of the vehicle.
In addition to the different performance requirements of front and rear tires, an additional difference evidences itself when the road surface is covered with rain or snow. Because the front tire of the vehicle generally precedes the rear tire, and the rear tire generally tracks the front tire, the road condition immediately preceding the rear tire is affected by the front tire. Heretofore this difference has gone largely ignored by tread designers and performance of the rear tire has not been optimized.